(1) Field of the Invention
The present invention relates to an optical print head (PH) and an image forming apparatus, and particularly to an art of increasing resolution without increasing the device size.
(2) Related Art
In recent years, there have been proposed optical PHs in order to reduce the size and the cost of image forming apparatuses using organic light-emitting diodes (OLEDs). Since it is possible to form, on the same substrate, the OLEDs and thin-film transistors (TFTs) that supply a driving current to the OLEDs, the cost reduction of the optical PHs can be achieved.
Unfortunately, an amount of light emitted by the OLEDs decreases in accordance with an accumulated light-emitting period and luminescence intensity during thereof. For this reason, application of OLEDs to optical PHs causes unevenness in degree of decrease in light amount between pixels caused by unevenness in accumulated light-emitting period of the OLEDs and luminescence intensity during thereof between pixels depending on each image to be written. This might deteriorate the image quality.
In response to this problem, there has been proposed an art of adjusting a light amount of OLEDs by adjusting a gate voltage of TFTs that supply a driving current to the OLEDs (see Japanese Patent Application Publication No. 2006-056010 for example). This adjustment of the gate voltage corrects unevenness in light amount between the OLEDs and temporal deterioration of the OLEDs.
Similarly, in response to a problem of unevenness in degree of decrease in light amount between the OLEDs due to environmental temperature of the OLEDs, the adjustment of the gate voltage also allows the OLEDs to emit light of a uniform light amount.
Note that a relation between an amount of a driving current to be supplied to each of the OLEDs and an amount of light emitted by the OLED is hereinafter referred to as light-emitting properties.